EMAT driver circuit has typically used a push-pull topology as illustrated in FIG. 1. This circuit provides a tone burst of current consisting of a specified number of cycles in the EMAT transmitter coil.
In the past EMATS (electromagnetic acoustic transducers) have typically used a push-pull topology. This type of circuit provides a tone burst of current consisting of a specified number of cycles in the EMAT transmitter coil. The system would be switched on for a period of time and then switched off for a period of time, followed by the switching on for the same period of time another coil to avoid saturation of the transformer and then switching it off at the end of the cycle. This cycle produces a square wave output that can be transformed into the voltage required to drive the EMAT and its tuning components.
The operation of the push pull is: switch Q1 on for a period of time and then switch off Q11 for a period of time, followed by the switching of Q2 on for the same period of time to avoid saturation of transformer and then switch off at the end of the cycle. This produces a square wave output that can be transformed to the voltage required to drive the EMAT and its tuning components. However, the transformer substantially limits the range of frequencies for which sufficient drive current can be produced. The parasitic components such as stray capacitance and leakage inductance associated with the transformer can also consume power and limit the current that would otherwise be delivered to the EMAT. Furthermore, the transformer can saturate if it is pulsed in patterns other than a symmetric tone burst, thereby limiting the power delivered to the EMAT. Also, the push pull topology cannot be used to quench the ringing of the EMAT or reflections of power from the transmission line between the pulser and the EMAT. Finally the output transformer adds to the size, weight and cost of the pulser, particularly when low frequency excitations are required and the transformer cores are relatively large.